Britain joined the U.S. and its allies in the fight against ISIS -- but any mission will come with a huge price tag .

The UK parliament has approved airstrikes in Iraq against the terror group which prime minister David Cameron has called one of `` staggering '' brutality .

Cameron had said Britain should join international allies in combating ISIS , an action that he warned would `` take not just months , but years . ''

While the total cost will depend on the intensity and length of operation , past experience can give some guidance , Malcolm Chalmers , research director from the Royal United Services Institute said .

Chalmers pointed to the UK 's seven month involvement in Libya through 2011 , which cost around $ 390 million , including missiles and flight hours .

The bill is additional to standard defense budgets , which include staffing costs and weapons spend . Last year , the UK defense budget was $ 60 billion .

Chalmers said he would expect the cost of ISIS airstrikes to be in the `` ballpark , '' of the Libya operation , `` assuming we only use air power and the campaign lasts for a couple of years . ''

Cameron has said that the mission against ISIS could last `` years . '' However , it is U.S.-led rather than the operation in Libya , in which European countries took the lead .

` Unique ' missiles

Cameron , in Friday 's debate aimed at convincing parliament to approve airstrikes , said Britain has `` unique assets '' no other coalition ally can contribute .

Cameron named the Brimstone precision missile , which he said minimized risk of civilian casualties , as one only Britain could contribute . The missiles can target convoys as well as fast moving , fleeting targets that were previously harder to strike , according to IHS Jane 's senior weapons analyst Ben Goodlad .

The Brimstone , which travels at supersonic speed , is a 1.8-meter missile weighing just under 50 kg . Advanced radar equipment enables it to guides itself to the target , so pilots do n't need to maneuver to release it . IHS Jane 's estimates each missile costs around $ 240,000 .

Brimstone missiles are compatible with the UK 's Tornado GR4 aircraft . The aircraft were used by British troops for relief missions in northern Iraq just over a month ago . Six of these are ready for deployment at the UK 's RAF base in Cyprus .

Flying the Tornadoes costs around $ 57,000 per hour , according to information released in a parliamentary debate about Libya in 2011 . From the Cyprus base , the aircraft could reach Iraq in just over an hour .

Goodlad said the RAF also has Tornado 's Storm Shadow cruise missiles , which cost $ 1.3 million each , and submarine-launched Tomahawk cruise missiles . These can be used to target areas that ca n't be accessed by planes , for example due to defenses , and cost round $ 1.5 million each .

U.S. forces have been using Tomahawk missiles for airstrikes in Syria earlier this week -- dropping 47 of them on Monday evening .

In total , the U.S. has conducted 20 strikes in Syria and 198 in Iraq from August 8 through September 23 .

Many of those operations were n't included in the Pentagon 's daily average spending figure of $ 7.5 million at the end of last month .

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UK can start bombing ISIS within hours , as it has six fighter jets on standby in Cyprus

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British forces have Brimstone precision missiles , high-tech weapons others do n't have

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The U.S. is leading the airstrikes against ISIS in Iraq and Syria